Can Spoilage Associated with H₂S Production and Black Inner Surface

Blackening of the inner surface of the can due to the production of H₂S gas occurs mainly in:

Correct Answer: Sulphur Stinker Spoilage

Sulphur stinker spoilage is characterised by blackening of the inner surface of the can due to the production of hydrogen sulphide (H₂S) gas, which reacts with the iron of the can to form black iron sulphide (FeS).

Causative Organism

• Clostridium nigrificans (also known as Desulfotomaculum nigrificans) — a thermophilic, anaerobic, sulphate-reducing spore-former.

Characteristics

• H₂S gas has a characteristic rotten-egg odour.
• H₂S reacts with the iron in the tinplate: Fe + H₂S → FeS (black precipitate) → black inner can surface.
• The can does NOT swell (H₂S is absorbed by iron to form FeS, so no gas pressure builds).
• Product is completely unacceptable — blackened and foul-smelling.

All Four Key Can Spoilage Types

• Flat Sour → B. coagulans, B. stearothermophilus → sour, no swell
• TA Spoilage → C. thermosaccharolyticum → swell + sour
• Sulphur Stinker → C. nigrificans → H₂S + black inner surface, no swell
• Hydrogen Swell → chemical (acid + tin) → H₂ gas, swell